#include<stdio.h>
#include<string.h>

void JsSort(char s[]);

int main()
{
	char s[80];
	gets(s);
	JsSort(s);
	printf("%s\n",s);
}

void JsSort(char s[])
{
	int l,i,j,k;
	char t;
	l = strlen(s);
	
	for(i=1;i<l-2;i+=2)
	{
		k = i;
		for(j=i+2;j<l;j+=2)
			if(s[k] < s[j])		k = j;
		if(k!=i)
		{
			t = s[k];
			s[k] = s[i];
			s[i] = t;
		}
	}
}
